In rugby, a scrum is a method of restarting play after a minor infringement of the Laws or when the ball becomes unplayable in a ruck or maul). The scrum serves to concentrate all the forwards and the scrum-halves in one place on the field, providing the opportunity for the backs to mount an attack using the space created elsewhere. The purpose of a scrum is to gain possession of the ball. Here are some key points about scrums in rugby:

• A scrum involves up to eight players from each team, known as the pack or forward pack, binding together in three rows).
• The ball is thrown into the middle of the tunnel between the two front rows, at which point the two hookers can compete for the ball, attempting to hook the ball back in the direction of their team-mates.
• Once possession has been secured, a team can keep the ball on the ground and in the scrum and attempt to drive the opposition down field. Alternatively, they can bring the ball to the hindmost foot of the scrum, where the ball is then passed into the backline and open play resumes again.
• The scrum-half is the key player at the scrum. This player throws the ball into the scrum, moves to the hindmost foot of the scrum, and is usually the player who picks the ball up and passes out to the fly-half who then distributes the ball to the backline.
• Scrums are one of the most dangerous phases in rugby, since a collapse or improper engage can lead to a front row player damaging or even breaking their neck. For this reason, only trained players may play in the front row to help avoid injuries).

In summary, the purpose of a scrum in rugby is to restart play after a minor infringement and gain possession of the ball. It involves up to eight players from each team binding together in three rows and competing for the ball. The scrum serves to concentrate all the forwards and the scrum-halves in one place on the field, providing the opportunity for the backs to mount an attack using the space created elsewhere.